The four categories of grading of the legendary swords are subdivided into so-called Wazamono [Grade Swords] of unknown number, the 49 Ryo Wazamono [Skillful Grade Swords], the 21 O Wazamono [Great Grade Swords] and the 12 Saijo O Wazamono [Supreme Grade Swords].
For the grading of the swords, there are Wazamono [Grade Swords], which are an unknown number of sharp Grade Swords of the lowest grade possible for a Meito blade. Shigure currently owned by Tashigi and Sandai Kitetsu currently owned by Roronoa Zoro are both Wazamono blades.
Ryo Wazamono [Skillful Grade Swords] are blades of higher quality than normal Grade Swords. There are 49 Skillful Grade Swords [previously 50, before Yubashiri was destroyed] in the world of One Piece.
Confirmed Ryu Wazamono swords are Kashu and Yamaoroshi, both currently owned by Tashigi and Yubashiri previously owned by Roronoa Zoro before it was destroyed.
O Wazamono [Great Grade Swords], are 21 Great Grade Swords of a very high level in quality. Only eclipsed by the Saijo O Wazamono [Supreme Grade Swords]. These blades which are confirmed to be of great grade are Nidai Kitetsu [meaning Second Generation Demon Splitter] currently owned by Tenguyama Hitetsu, Wado Ichimonji and Enma both owned by Roronoa Zoro, Shusui returned back to Shimotsuki Ryuma and Ame no Habakiri currently owned by Kozuki Momonosuke.
Saijo O Wazamono [Supreme Grade Swords] are the 12 Supreme Grade Swords of the highest quality. Confirmed to be of supreme grade are, Yoru owned by Dracule Mihawk, Shodai Kitetsu [meaning First-generation Demon Splitter] owned by the bald member of Five Elders and Murakumogiri owned by Whitebeard before his death.
Then there are also unclassified Meitos, these are blades that have been confirmed as Meito, but their grade hasn’t been specified yet. These swords are Raiu currently owned by Shiryu, Durandal currently owned by Cavendish, Shirauo currently owned by Charlotte Amande and Pretzel currently owned by Charlotte Cracker.